1. Field of the Invention
The present invention relates to an apparatus for hot-probing integrated semiconductor circuits on wafers.
2. Description of the Background Art
Integrated semiconductor circuits are used in engine and transmission sections of automobiles, for example, where they are exposed to continuously changing temperature ranges reaching temperatures of 300° C. The thermal stresses must be taken into account as early as the manufacture and testing of the integrated semiconductor circuits. Once integrated semiconductor circuits have been fabricated, they undergo functional verification in a test step while they are still integrated in the wafer, which is to say before singulation.
The goal of the test process is to test the electrical functionality of the circuits at temperatures of up to 300° C. Testing at these temperatures is referred to as hot-probing of the wafer.
An apparatus for hot-probing the wafers includes a movable support device for the wafers, known as a hot chuck, upon which the wafers are heated to the desired temperatures. In addition, the apparatus for hot-probing contains a measurement card with electronic circuits arranged thereupon, by which the functionality of the integrated semiconductor circuits on the wafer can be checked. Arranged on the underside of the measurement card and connected in a force-locking manner thereto by a retaining mechanism is a test head with contact needles, referred to as a spider. The contact needles establish the electrical contact between the measurement card and the semiconductor circuits to be tested on the wafer. Once the wafer has been positioned, by the movable support device, beneath the test head at the correct point (in the x and y positions), the support device is moved upward (z position) and the contact needles penetrate the contact layer, which preferably is designed as an aluminum layer. In this context, an insulating metal oxide layer on the surface must be overcome when contact is made, especially in the case of contact surfaces containing aluminum. After the function of one integrated semiconductor circuit has been tested, the wafer is advanced to the next component, and contact is made again, until the desired circuits have been measured. During contact, the electronic circuits on the measurement card transmit test signals and evaluate the response signals coming back from the individual integrated semiconductor circuits on the wafer.
As a result of the high test temperatures, the measurement card and the associated electronics are exposed to very high stresses, which can significantly reduce the service life of the testing apparatus and, in particular, can lead to distortion of the electrical measurement results. Moreover, the measurement card deforms under the influence of heat, so that bending can occur in the center of the measurement card and the contact needles move out of the contact areas. Consequently, the apparatus must be readjusted, resulting in time losses and added costs.
DE 100 60 437 A1 teaches a needle card arrangement for parallel testing of a plurality of integrated circuits on a wafer, comprising a printed circuit board and a measurement card with multiple electronic circuit systems known as BOST (Build Outside Self Test) modules for functional verification of the integrated semiconductor circuits on the wafers. With the aid of test pattern generators, the BOST modules provide test signals to contact needles, which establish an electrical contact between the measurement card and the integrated semiconductor circuits. Provided between the printed circuit board and measurement card are heat dissipating means, or intermediate layers between the printed circuit board and measurement card, or openings in the printed circuit board for delivery of a coolant fluid. However, the means employed serve only to dissipate the waste heat generated by the BOST modules in operation; they are not suitable for removing the great heat produced by the hot chucks during hot-probing of wafers and thereby protecting the measurement card from the effects of heat.
In addition, WO 00/19215, which corresponds to U.S. Pat. No. 6,081,110 discloses a test apparatus for probing integrated semiconductor circuits on wafers that has a support device (chuck) for wafers that contains a heater for heating the support device and the wafers. While the support device for the wafers is arranged to be horizontally movable, the performance board and the measurement card with the electronic circuit systems for functional verification of the integrated semiconductor circuits on the wafers is rigidly fixed in place in the test apparatus. In order to avoid deformation of the measurement card under the influence of heat, a heat shield plate is screw-mounted by an annular insert to the housing of the apparatus and also to the measurement card, which includes a test head with contact needles. Moreover, the annular insert is also rigidly connected by a mechanical connector to the part of the test apparatus that contains the units for supplying electricity to the measurement card and the analysis units. The heat shield plate consists of a composite material that contains primarily aluminum. In addition, the heat shield plate has two different surfaces, one of which has a low absorptivity and the other of which has a low emissivity. However, since aluminum has a high coefficient of thermal expansion, quite high thermal deformations can occur in the plate center, or else high stresses if the plate is very stiff. Another disadvantage of this arrangement is that replacement of the measurement card, which is necessary for each change in the arrangement of the semiconductor circuits on the wafer, is very time-consuming and thus very costly, since the screw connections between the heat shield plate and either the measurement card or the test apparatus must be detached.
US 2004/0119463 A1 discloses an arrangement for a measurement card with a test head and contact needles which has flow paths for a fluid. Attached to the underside of the measurement card is a cover that encloses the space between the measurement card and contact needles. On account of the pressure differences, the fluid flows in through an opening on the top of the measurement card arrangement, passes through the flow paths, flows into the space between the measurement card and contact needles, and exits this space through gaps present between the contact needles and the cover. As fluid, compressed air or dry nitrogen are used. In this context, heat is to be supplied to or removed from the measurement card arrangement as needed. However, this arrangement is only suitable for heating or cooling the region of the contact needles or the region of the measurement card that is directly traversed by the flow paths. Cooling of the entire measurement card, which typically has very sensitive electronic circuits, is not achieved.